The present invention relates to a recording medium which comprises a first substance and a second substance at least, and in which an external energy is applied to at least one of the first and second substances to react with each other, thereby varying their optical characteristics to record information.
Conventionally, there has been proposed a recording medium which includes a first substance and a second substance, and in which the first and second substances cause an oxidation-reduction reaction by being irradiated with an external energy, for example, a laser beam, thereby varying the optical characteristic to record information.
For example, U.S. Pat. No. 5,459,018 discloses a recording medium in which metal, such as Al and Fe, is used as a first substance, and oxide, such as TeO2 and In2O3, is used as a second substance. These substances coexist to make a single-layered film, or are laminated alternately to make a laminated film.
By the way, according to the investigation carried out by the inventors of the present invention, when the recording medium utilizes the oxidation-reduction reaction between the first substance and the second substance as set forth in the aforementioned prior art, the reaction of the first and second substances develop in the middle of the film formation because the first and second substances both have reactivities. As a result, there arises a possibility of decreasing overall reflectance. Further, in such a recording medium, the first and second substances react with each other when the external energy is not applied (when information is not recorded). Thus, it is expected that the retention of the recorded information deteriorates due to chronological degradation. In an actual application, it is believed that there arise problems when the recording medium is used as an ordinary recording medium.
Furthermore, according to the further investigation carried out by the inventors of the present invention, in order to obtain high reflectance, it is necessary to use a substance of good reflectance as a substance which carries out the reaction when the external energy is applied (when information is recorded). However, because of the good reflectance, the substance exhibits small absorptance to the external energy. As a result, the substance absorbs less heat which is required for the reaction, because it is of good reflectance. Accordingly, it is preferred that the first and second substances are a combination which shows good reactivity when information is recorded. However, the combination showing good reactivity causes unnecessary reactions when the films are formed as aforementioned or when information is not recorded. Thus, the possibility increases in that the recording characteristics of the recording medium degrade.
The present invention has been developed in view of the aforementioned problems. Therefore, in a recording medium which includes a first substance and a second substance at least, the first and second substances undergoing an oxidation-reduction reaction when an external energy is applied thereto, thereby recording information by varying the optical characteristics, it is therefore an object of the present invention to suppress the reaction of the first and second substances, reaction which degrades the recording characteristics other than the case where the recording medium is subjected to recording.
While investigating into a recording medium which includes a first substance and a second substance at least, and which record information by varying the optical characteristics by applying an external energy, the present invention has been completed by elaborating the combination of the first substance and the second substance which undergo an oxidation-reduction reaction, and by diligently studying a third substance which suppresses the reactivities of the first and second substances.
For example, the present recording medium is characterised in that it is a recording medium for recording information by varying optical characteristics thereof by applying an external energy thereto, which includes:
a first substance and a second substance which cause an exothermic reaction to vary optical characteristics of said first and second substances when the external energy is applied, said first substance undergoing oxidation in a wide sense; and said second substance undergoing reduction in a wide sense; and
a third substance interposed between said first substance and said second substance, enabling said first substance and said second substance to react when said external energy is applied, and suppressing said first substance and said second substance to react when said external energy is not applied.
When the external energy is applied to the present recording medium, the first substance reduces the second substance with the first substance and the second substance passing through the third substance and/or destroying the third substance. And, the first substance itself undergoes the oxidation in a wide sense. Thus, the first substance and the second substance undergo an oxidation-reduction reaction. Due to the reaction, at least a part of the first and second substances vary the optical characteristics, and thereby information is recorded in the present recording medium.
Then, since the third substance is interposed between the first substance and the second substance, the aforementioned oxidation-reduction reaction is suppressed when forming films or when the external energy is not applied (when information is not recorded).
Further, since the oxidation-reduction reaction is an exothermic reaction, the resulting modified reaction products are stable energetically, and the reverse reaction is less likely to occur. Hence, the present recording medium can suppress the reaction between the first and second substances which degrades the recording characteristics.
Said first substance can be at least one member selected from the group consisting of metals, intermetallic compounds, nitrides, carbides, silicides, borides, sulfides, selenides, tellurides, phosphides, arsenides, antimonides and substances containing these members. The members generate an energy of 1,000 kJ or more when bonding with oxygen molecules in an amount of 1 mol (hereinafter referred to as an xe2x80x9coxygen-bonding energyxe2x80x9d), and contain at least one element selected from the group consisting of elements of group 1 of the periodic table of the elements, elements of group 2 thereof, elements of group 3 thereof, elements of group 4 thereof, elements of group 5 thereof, Cr, Mn, Zn, Al and Si.
The elements of group 1 can be Li, Na, K, etc. The elements of group 2 can be Mg, Ca, etc. The elements of group 3 can be Sc, Y, etc. The elements of group 4 can be Ti, Zr, etc. The elements of group 5 can be V, Nb, etc.
Said second substance can be at least one member selected from the group consisting of oxides, substances containing oxygen as a constituent element, substances with oxygen adsorbed, compounds thereof or mixtures thereof. The members require an energy of 550 kJ or less when dissociating oxygen molecules in an amount of 1 mol (hereinafter referred to as an xe2x80x9coxygen-dissociating energyxe2x80x9d).
The second substance gives oxygen to the first substance to oxidize it, and is itself likely to be reduced. The second substance can be a substance containing at least one member selected from the group consisting of oxides and substances containing oxygen as a constituent element. The members contain at least one element selected from the group consisting of elements of group 6 of the periodic table of the elements, elements of group 8 thereof, elements of group 9 thereof, elements of group 11 thereof, Ti, V, Mn, Ni, Re, Ge, Sn, Pb, As, Sb, Bi, Se, Te, Ce, Pr and Tb.
Here, the elements of group 6 can be Cr, Mo, etc. The elements of group 8 can be Fe, Ru, etc. The elements of group 9 can be Co, Rh, Ir, etc. The elements of group 11 can be Cu, Ag, Au, etc.
According to the investigations carried out by the inventors of the present invention, when the oxygen-bonding energy of the first substance is less than 1,000 kJ, the first substance is less likely to bond with the oxygen, and the reactivity decreases. Moreover, when the oxygen-dissociating energy of the second substance is more than 550 kJ, the oxygen is less likely to dissociate, and the reactivity decreases. Accordingly, the first and second substance can preferably have the aforementioned respective energy ranges.
Further, the first substance can be a substance containing at least one member selected from the group consisting of metals, intermetallic compounds, nitrides, carbides, silicides, borides, sulfides, selenides, tellurides, phosphides, arsenides, antimonides and substances containing these members. The members generate an oxygen-bonding energy of 500 kJ or more, and exhibit a melting point or a decomposition temperature of from 100xc2x0 C. or more to 300xc2x0 C. or less. And, the second substance can be a substance containing at least one member selected from the group consisting of oxides, substances containing oxygen as a constituent element, substances with oxygen adsorbed, compounds thereof and mixtures thereof. The members require an oxygen-dissociating energy of 550 kJ or less.
Furthermore, the second substance gives oxygen to the first substance to oxidize it, and is itself likely to be reduced. The second substance can be a substance containing at least one member selected from the group consisting of oxidea and substances containing oxygen as a constituent element. The members contain at least one element selected from the group consisting of elements of group 6 of the periodic table of the elements, elements of group 8 thereof, elements of group 9 thereof, elements of group 11 thereof, Ti, V, Mn, Ni, Re, Ge, Sn, Pb, As, Sb, Bi, Se, Te, Ce, Pr and Tb.
Here, the elements of group 6 can be Cr, Mo, etc. The elements of group 8 can be Fe, Ru, etc. The elements of group 9 can be Co, Rh, Ir, etc. The elements of group 11 can be Cu, Ag, Au, etc.
By having the first substance exhibit a melting point or a decomposition temperature in the aforementioned range, the first substance can be turned into a liquid phase by a small external energy. The aforementioned oxidation-reduction reaction is a reaction between the liquid phase and the solid phase so that the reactivity is enhanced compared with the reaction between the solid phases. When the substance constituting the first substance exhibits a melting point or a decomposition temperature of less than 100xc2x0 C., the heat resistance of recorded data decreases. When the melting point or the decomposition temperature exceeds 300xc2x0 C., a large external energy is required unpreferably.
Moreover, by having the first substance exhibit a melting point or a decomposition temperature in the aforementioned range, the reactivity is enhanced. Accordingly, the oxygen-bonding energy of the first substance can be decreased, and is 500 kJ or more. According to the investigations carried out by the inventors of the present invention, when the oxygen-bonding energy is less than 500 kJ, the reactivity is decreased unpreferably.
Note that, even when the third substance is interposed, the first substance and the second substance cause the oxidation-reduction reaction, at least a part of the first and second substances are modified to vary the optical characteristics. Thus, information is recorded. And, even when the first substance and the second substance are made into the aforementioned combination of good reactivity, the interposing third substance can suppress the reaction between the first and second substances, reaction which degrades the recording characteristics other than the case where the recording medium is subjected to recording.